The present invention relates to a stripper mechanism for electrostatographic printing machines and more particularly to a stripper member for stripping a print substrate from a fuser member.
In an electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photo conductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive area. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the photoconductive insulating member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
One of the more conventional approaches to fixing the toner image is through the use of heat and pressure by passing the print substrate containing the unfused toner images between a pair of opposed roller members at least one of which is internally heated. During this procedure, the temperature of the electroscopic toner material is elevated to a temperature at which the toner material coalesces and becomes tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to become bonded to the support member. Typical of such fusing devices are two roll systems wherein the fuser roll is coated with an abhesive material such as a silicone rubber or other low surface energy elastomer. The silicone rubbers that can be used as the surface of the fuser member include room temperature vulcanizable silicones referred to as RTV silicones liquid injection moldable or extrudable silicone rubbers and high temperature vulcanizable silicones referred to as HTV silicones.
During the fusing process and despite the use of low surface energy materials as the fuser roll surface, there is a tendency for the copy print substrate to remain tacked to the fuser roll after passing through the nip between the fuser roll and the pressure roll. When this happens, the tacked print substrate does not follow the normal substrate path but rather continues in an arcuate path around the fuser roll, eventually resulting in a paper jam which will require operator involvement to remove the jammed paper before any subsequent imaging cycle can proceed. As a result it has been common practice to use one or more techniques to ensure that the print substrate is stripped from the fuser roll downstream of the fuser nip. One of the common approaches has been the use of a stripper finger or a plurality of stripper fingers placed in contact with the fuser roll to strip the print substrate from the fuser roll. While satisfactory in many respects, this suffers from difficulties with respect to both fuser roll life and print quality. To ensure an acceptable level of stripping it is frequently necessary to load such a stripper finger against the fuser roll with such a force and at such an attack angle that there is a tendency to peel the silicone rubber off the fuser roll thereby damaging the roll to such an extent that it can no longer function as a fuser roll. In addition, since the finger comes in contact with the surface of the print substrate which has hot, just fused toner image there is a tendency for the stripper finger to scrape toner from the print substrate thereby creating a copy quality defect in the form of a line which may be the width of the stripper finger. Furthermore, while a stripper finger may only slightly deform the toner this may create a defect in the form of a stripe of higher gloss than the rest of the print. It has also been found that stripper fingers typically made of high energy materials become contaminated with toner on the side in contact with the fuser roll eventually resulting in the stripper finger lifting off the fuser roll and resulting in paper jams. As a result of the difficulties associated with stripper fingers use has been taken in many instances of air stripping systems. While satisfactory in many respects, the air stripping systems are typically very expensive involving elaborate air delivery mechanisms.